1. Field of the Invention
This invention relates to turbomachinery and is particularly directed to integrated auxiliary power and environmental control units for aircraft and the like.
2. Description of the Prior Art
In large aircraft, it has been the custom, heretofore, to provide an auxiliary power unit, comprising a prime mover driving a compressor, which served to provide compressed air for powering the airplane air cycle environmental control unit, or for powering the airplane engine air starters. In passenger planes, it has been customary to also provide an environmental control unit for cooling, heating and pressurization of the passenger compartment. This unit has comprised a turbine which may be driven either by bleed air from the airplane's propulsion engines or by compressed air provided by a separate prime mover (auxiliary power unit). The prime mover mechanically drives a compressor for providing additional air flow to the environmental control unit turbine, to provide both the proper aircraft ventilation rate and provide an energy source for the environmental control cycle. Air flow from the environmental control unit turbine is also provided to the aircraft cabin at the desired temperature and pressure. It has been conventional, heretofore, to drive the compressor of the environmental control unit at maximum output to provide a maximum flow rate for the limiting heating or cooling condition and adjust the output flow temperature by flow mixing through a temperature control valve. In large passenger planes, it has been customary to provide a plurality of independent environmental control units.
It will be apparent that, where a plurality of independent environmental control units are provided, it is also necessary to provide a corresponding plurality of sensor and control systems. It should also be noted that, with the systems of the prior art, it has been necessary to operate each of these environmental control unit compressors at maximum output at all times, regardless of the actual demand, in order to be able to accommodate a range of potential demands. Obviously, this is not energy efficient.